Sebastian Markbåge
368202181e
This doesn't change production behavior. We always render Iterables to our best effort in prod even if they're Iterators. But this does change the DEV warnings which indicates which are valid patterns to use. It's a footgun to use an Iterator as a prop when you pass between components because if an intermediate component rerenders without its parent, React won't be able to iterate it again to reconcile and any mappers won't be able to re-apply. This is actually typically not a problem when passed only to React host components but as a pattern it's a problem for composability. We used to warn only for Generators - i.e. Iterators returned from Generator functions. This adds a warning for Iterators created by other means too (e.g. Flight or the native Iterator utils). The heuristic is to check whether the Iterator is the same as the Iterable because that means it's not possible to get new iterators out of it. This case used to just yield non-sense like empty sets in DEV but not in prod. However, a new realization is that when the Component itself is a Generator Function, it's not actually a problem. That's because the React Element itself works as an Iterable since we can ask for new generators by calling the function again. So this adds a special case to allow the Generator returned from a Generator Function's direct child. The principle is “don’t pass iterators around” but in this case there is no iterator floating around because it’s between React and the JS VM. Also see #28849 for context on AsyncIterables. Related to this, but Hooks should ideally be banned in these for the same reason they're banned in Async Functions.
React · 
React is a JavaScript library for building user interfaces.
- Declarative: React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes. Declarative views make your code more predictable, simpler to understand, and easier to debug.
- Component-Based: Build encapsulated components that manage their own state, then compose them to make complex UIs. Since component logic is written in JavaScript instead of templates, you can easily pass rich data through your app and keep the state out of the DOM.
- Learn Once, Write Anywhere: We don't make assumptions about the rest of your technology stack, so you can develop new features in React without rewriting existing code. React can also render on the server using Node and power mobile apps using React Native.
Learn how to use React in your project.
Installation
React has been designed for gradual adoption from the start, and you can use as little or as much React as you need:
- Use Quick Start to get a taste of React.
- Add React to an Existing Project to use as little or as much React as you need.
- Create a New React App if you're looking for a powerful JavaScript toolchain.
Documentation
You can find the React documentation on the website.
Check out the Getting Started page for a quick overview.
The documentation is divided into several sections:
- Quick Start
- Tutorial
- Thinking in React
- Installation
- Describing the UI
- Adding Interactivity
- Managing State
- Advanced Guides
- API Reference
- Where to Get Support
- Contributing Guide
You can improve it by sending pull requests to this repository.
Examples
We have several examples on the website. Here is the first one to get you started:
import { createRoot } from 'react-dom/client';
function HelloMessage({ name }) {
return <div>Hello {name}</div>;
}
const root = createRoot(document.getElementById('container'));
root.render(<HelloMessage name="Taylor" />);
This example will render "Hello Taylor" into a container on the page.
You'll notice that we used an HTML-like syntax; we call it JSX. JSX is not required to use React, but it makes code more readable, and writing it feels like writing HTML.
Contributing
The main purpose of this repository is to continue evolving React core, making it faster and easier to use. Development of React happens in the open on GitHub, and we are grateful to the community for contributing bugfixes and improvements. Read below to learn how you can take part in improving React.
Code of Conduct
Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.
Contributing Guide
Read our contributing guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React.
Good First Issues
To help you get your feet wet and get you familiar with our contribution process, we have a list of good first issues that contain bugs that have a relatively limited scope. This is a great place to get started.
License
React is MIT licensed.